perfect number
nounEtymology Calque of Latin numerus perfectus, with this use of perfectus itself a semantic loan from Ancient Greek τέλειος (téleios).
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Mathematics, Number theory, Sciences A number that is the sum of all of its divisors except itself.
- The factors of 6 are 1, 2, 3 and 6, and 1 + 2 + 3 = 6, so 6 is a perfect number.
- The factors of 28 are 1, 2, 4, 7, 14 and 28, and 1 + 2 + 4 + 7 + 14 = 28, so 28 is a perfect number.
- Derived terms
- hyperperfect number
- Related terms
- abundant number, amicable numbers, deficient number, Mersenne prime, sociable numbers